Can not select any linked element in revit using revit api

[jackmrdoctor]

using Autodesk.Revit.Attributes;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;
using Autodesk.Revit.UI.Selection;
using System;
using System.Collections.Generic;
using System.IO;

[Transaction(TransactionMode.Manual)]
public class FixtureHandOrientationAndLocationCommand : IExternalCommand
{
public Result Execute(
ExternalCommandData commandData,
ref string message,
ElementSet elements)
{
try
{
// Get the active document
Document doc = commandData.Application.ActiveUIDocument.Document;
UIDocument uiDoc = commandData.Application.ActiveUIDocument;

if (uiDoc == null || uiDoc.Selection == null)
{
message = "No active selection available.";
return Result.Failed;
}

// Prompt the user to select linked instances
IList<Reference> pickedRefs = uiDoc.Selection.PickObjects(ObjectType.LinkedElement, new LightingFixtureSelectionFilter(), "Select linked lighting fixture instances");
if (pickedRefs.Count > 0)
{
foreach (Reference pickedRef in pickedRefs)
{
// Get the linked instance
RevitLinkInstance linkInstance = doc.GetElement(pickedRef) as RevitLinkInstance;
if (linkInstance == null)
{
message = "Selected element is not a linked instance.";
return Result.Failed;
}

Document linkedDoc = linkInstance.GetLinkDocument();
if (linkedDoc == null)
{
message = "Failed to access linked document.";
return Result.Failed;
}

ElementId linkedElementId = pickedRef.LinkedElementId;
Element linkedElement = linkedDoc.GetElement(linkedElementId);
if (linkedElement == null || !(linkedElement is FamilyInstance fixture))
{
message = "Selected element is not a linked family instance.";
return Result.Failed;
}

// Check if the fixture has a valid location
LocationPoint fixtureLocation = fixture.Location as LocationPoint;
if (fixtureLocation != null)
{
// Get the center of the fixture
XYZ center = fixtureLocation.Point;

TaskDialog.Show("Fixture Location",

$"Location (XYZ): {center.X:F2}, {center.Y:F2}, {center.Z:F2}");
}
else
{
message = "One or more selected fixtures do not have valid locations.";
return Result.Failed;
}
}
return Result.Succeeded;
}
else
{
message = "No elements selected.";
return Result.Failed;
}
}
catch (Exception ex)
{
message = $"Error: {ex.Message}";
return Result.Failed;
}
}

}
public class LightingFixtureSelectionFilter : ISelectionFilter
{
[Obsolete]
public bool AllowElement(Element elem)
{
if (elem.Category.Name == "Lighting Fixtures")
{

return true;

}
return false;
}

public bool AllowReference(Reference reference, XYZ position)
{
return true;
}
}
i can not select revitlinkinstance that in category "Lighting Fixtures"
if i delete LightingFixtureSelectionFilter() in
IList<Reference> pickedRefs = uiDoc.Selection.PickObjects(ObjectType.LinkedElement, new LightingFixtureSelectionFilter(), "Select linked lighting fixture instances");
it will work find but not what i want. so hard to work with revit link. 
the problem is from here

if (elem.Category.Name == "Lighting Fixtures")
{

return true;

}
seem to me revit can not get inside the if statement. even elem have bunch of element in category "Lighting Fixtures"

[scgq425 · Accepted solution]

Hi jackmrdoctor:

just implention ISelectionFilter , the input element is revitlinkinstance ,  u selection target category u need to in linkdoc not active document , so u can change u code to this  and run again :

```

public bool AllowElement(Element elem)
{
Instance = elem as RevitLinkInstance;
if (Instance != null) return true;

return false;
}

public bool AllowReference(Reference reference, XYZ position)
{
if (Instance == null)
{
return false;
}

var linkdoc = Instance.GetLinkDocument();
var familyInstance = linkdoc.GetElement(reference.LinkedElementId);
if (familyInstance.GetType() == typeof(Floor) || familyInstance.Category.Name == "Beams") return true;

return false;
}

```

[jackmrdoctor]

Thank you so much it works.